1. Field of the Invention
The present invention relates to increase control and increase stop control of a fuel injection amount of an internal combustion engine.
2. Description of the Related Art
In an internal combustion engine, so-called air/fuel ratio feedback control is carried out to keep the air/fuel ratio at a target air/fuel ratio. More specifically, an oxygen concentration in exhaust gas is detected by an oxygen concentration sensor provided in an exhaust system of the internal combustion engine, and the air/fuel ratio is calculated based on the detected oxygen ratio and the fuel injection amount. A feedback correction amount is determined to eliminate a deviation of the calculated air/fuel ratio and the target air/fuel ratio, thereby performing feedback control of the fuel injection amount.
In an automobile, a canister which adsorbs evaporated fuel in a fuel tank is provided, and canister purge (hereinafter, simply called “purge”) for desorbing the fuel adsorbed in the canister from an adsorbent and supplying the fuel to an intake system of the engine is carried out. On the occasion of the canister purge, a vapor concentration in the purge gas is learned, and based on the result, the fuel injection amount is corrected.
When the temperature of cooling water is low at the starting time of an engine or the like, the fuel injection amount is increased. However, when the fuel injection amount is increased, it is difficult to determine whether the change in the air/fuel ratio calculated by utilizing the oxygen concentration sensor is caused by the increase of the fuel injection amount, or by purge, and therefore, learning precision of the vapor concentration is reduced. On the other hand, when the canister purge is not performed while the fuel injection amount is being increased at cold time after the start of the engine or the like, there arises the problem that the purge cannot be executed early at the cold time of the engine.
A method of prohibiting execution of purge while the increase of fuel is performed at the cold time after the start of the engine is proposed in Japanese Patent Application Laid-open under No. 6-323177. A method of starting purge when the cooling water temperature is a predetermined value or higher is proposed in Japanese Patent Application Laid-open under NO. 2001-82264. Japanese Patent Applications Laid-open under Nos. 10-18883 and 6-26386 concerns the control of the fuel increase amount at the engine cold time and the purge starting time after the start of the engine.